1. Field of the Invention
The present invention relates to a conductive composition and a manufacturing process of conductive paste used as electronic device of multilayer structure.
2. Description of the Related Art
As the miniaturization of electric devices, it is required to provide more compact electronic components, such as inductors, capacitors, and filters, for use in such electronic devices. To maintain electronic characteristics and to achieve further miniaturization of electronic component, conductive filter is required to have a smooth surface and absolutely no pinhole. And metal particles in conductive composition are required for further reduction in size and higher dispersion. Aggregated metal particles and deformed metal particles at conductive paste forming internal electrodes of ceramics multilayer component may cause electric defective such as short. Particularly, at thin film multilayer electronic component, metal particles are required for further reduction in size and higher dispersion. When particle size of the aggregated metal particles becomes larger than film thickness of the internal electrodes, ceramics between the internal electrodes is greatly stressed, resulting in a marked reduction in the reliability and a lower yield of the ceramic laminated component.
Conventionally, as methods to disperse metal powders into a vehicle and an organic solvent, a method using media such as Laikai machine (a mixing and grinding machine), a triple roller or a ball mill, and a collision dispersion method which high pressure slurries collide among themselves are proposed. The collision dispersion method is disclosed in Japanese Patent Unexamined Publication 9-201521, Japanese Patent Unexamined Publication 9-299774, Japanese Patent Unexamined Publication 10-57789, PCT publication WO00/04559, Japanese Patent Unexamined Publication 10-887457 and Japanese Patent Unexamined Publication 11-1460511 or so.
However, media used disperse treating method, when particle of metal particles is submicron order or less, or when the metal particles are firmly aggregated, had a problem of not being able to make metal parties ultra-fine particles and disperse the particles uniformly. Further problem was excess action of medias deforming metal particles.
Moreover, collision dispersion method, after a drying step, had its limit for firmly aggregated metal particles to be sufficiently crushed and to be uniformly dispersed. And to disperse the firmly aggregated metal particles to a certain extent, lengthy treatment is required and a longer treating time and a great deal of energy should be spent. Accordingly, poor step efficiency and increased production costs bound to result.
Therefore, a process of preventing aggregation of the metal particles by wetting the metal particles is proposed (See Japanese Patent Unexamined Publication 2001-357720).
Moreover, when used as internal electrodes of multilayer form, to inhibit reaction at firing and to prevent occurrence of delamination, ceramics powder comprising conductive paste is proposed (See Japanese Patent Unexamined Publication 8-78267).
However, with conventional dispersing method, dispersion of metal particles as well as mixing and dispersion of metal parties slurry and ceramics particles slurry were not sufficient. Due to this, an electrode film formed by using conductive paste which is obtained by conventional method, had film thickness of insufficient uniformity preventing improvement for yield of the electronic component.
Further, due to the method of wetting the metal particles, aggregation of metal particles can be prevented, however, the metal particles were unlikely to be dispersed highly.